A judge in the US has rejected a defence bid to drop charges against six police officers, accused over the death of a black man, and ordered separate trials.

Freddie Gray died in April, a week after suffering a critical spinal injury while in custody. It led to protests and a riot in Baltimore.

The case has become part of a national debate in America on police treatment of minorities.

The six officers face charges ranging from second-degree murder to manslaughter, second-degree assault and misconduct.

Judge Barry Williams has also thrown out a request to remove the State’s Attorney and other prosecutors from the case.

Williams rejected the defence contention that the attorney violated her obligation to assure a fair trial when she announced the charges at a news conference as the largely black city of Baltimore of 620,000 people was in turmoil.

Williams said that point would best be settled in a misconduct proceeding, not in his courtroom. He said the attorney’s comments did not warrant dropping charges.